1. Field of the Invention
The present invention relates to a dynamic flow rate adjusting method for an injector.
2. Description of Related Art
An adjusting system shown in FIG. 1 adjusts a dynamic flow rate of an injector 1. The dynamic flow rate of fluid injected by the injector 1 is adjusted by regulating biasing force of a spring 21. The biasing force of the spring 21 is regulated by adjusting a press-fitting position of an adjusting pipe 23. The dynamic flow rate is quantity of fluid injected during a stroke (opening and closing motion) of a needle 30. The injector 1 injects experimental fluid through injection holes 25 when the needle 30 as a valve member separates from a valve seat 27. As the experimental fluid, incombustible fluid having substantially the same viscosity as the fuel is used in order to prevent ignition and the like. The spring 21 as a biasing member biases the needle 30 in a direction for seating the needle 30 on the valve seat 27, or a direction for closing the injection holes 25. The adjusting pipe 23 is driven to an inside of a housing 10 of the injector 1 when press-fitted. When the press-fitting position of the adjusting pipe 23 is determined and the target dynamic flow rate is achieved, the adjusting pipe 23 is fixed to the housing 10 by crimping and the like. If current is supplied to a coil 50 as an electric driving member, magnetic force is generated for attracting the needle 30 toward a fixed core 22 (upward in FIG. 1) against the biasing force of the spring 21. Thus, the needle 30 separates from the valve seat 27. A maximum lifting distance of the needle 30 is defined by the position of the fixed core 22.
A pump 100 draws the experimental fluid from a tank 101 to the injector 1. A pressure gauge 102 measures pressure of the fluid supplied to the injector 1. A flowmeter 103 as measuring means measures the flow rate of the fluid flowing through the injector 1. For instance, the flowmeter 103 outputs a pulse number of pulse signals generated per unit time in accordance with the flow rate, as a flow rate signal. The pulse number outputted by the flowmeter 13 increases as the flow rate increases. A back pressure valve 104 regulates the pressure of the fluid supplied to the injector 1 to a predetermined pressure. A pressure reducing valve may be employed instead of the back pressure valve 104. A motor gear 111 rotating with a motor 110 as an adjusting amount changing means is meshed with a screw gear 112. The screw gear 112 is connected with a driving screw 113 in thread engagement. If the screw gear 112 rotates, the driving screw 113 moves upward or downward in FIG. 1. If the driving screw 113 moves downward, the adjusting pipe 23 is driven to the inside of the housing 10. A personal computer (PC) 120 as calculating means receives the flow rate signal outputted by the flowmeter 103 and calculates the dynamic flow rate corresponding to the present press-fitting position of the adjusting pipe 23. The PC 120 controls a driving circuit 121 based on a difference between the calculated dynamic flow rate and the target dynamic flow rate. Thus, the PC 120 regulates controlling current supplied to the motor 110 from the driving circuit 121. The PC 120 calculates the press-fitting position of the adjusting pipe 23 for the next time.
If the adjusting pipe 23 is driven into the housing 10, the biasing force of the spring 21 is increased. If the adjusting pipe 23 is press-fitted, a valve opening period To of the injector 1 is lengthened, and a valve closing period Tc is contracted as shown in FIG. 9 in the case where the coil 50 is applied with the controlling pulse current having an identical frequency, an identical pulse width and an identical amplitude. Therefore, a time length of one injection performed by the injector 1 is contracted and the injection quantity is reduced. Accordingly, the dynamic flow rate calculated by the PC 120 based on the flow rate signal outputted by the flowmeter 103 is reduced. The valve opening period To is a time length from the time when an injection pulse signal for commanding the injection is turned on to the time when the needle 30 separates from the valve seat 27 and the needle 30 is stopped by the fixed core 22, so a lifting distance of the needle 30 is maximized. The valve closing period Tc is a time length from the time when the injection pulse signal is turned off to the time when the needle 30 is seated on the valve seat 27 and the injection is stopped. In FIG. 9, an axis qb represents the flow rate before the adjusting pipe 23 is press-fitted, and an axis qa is the flow rate after the adjusting pipe 23 is press-fitted.
A conventional adjusting method of the dynamic flow rate performed with the adjusting pipe 23 will be explained based on FIGS. 10 and 11. In FIG. 10, an axis of abscissas represents the press-fitting degree L of the adjusting pipe 23 and an axis of ordinates represents the dynamic flow rate q. A symbol qt on the axis q represents the target dynamic flow rate. The press-fitting degree L as an adjusting amount of the adjusting pipe 23 represents displacement of the adjusting pipe 23 from an initial position to the position where the adjusting pipe 23 is press-fitted. In the case where a plurality of injectors 1 having identical structure are adjusted, an average value of a rate of change (a change rate Kq) of the dynamic flow rate q with respect to the press-fitting degree L of the adjusting pipe 23 is calculated in advance from measurements of the injectors 1. Then, the press-fitting degree L of the adjusting pipe 23 for achieving the target dynamic flow rate qt is calculated based on the change rate Kq.
However, the dynamic flow rate q includes a dynamic flow rate error Ed and a static flow rate error Es of a static flow rate as shown in FIG. 10. Therefore, if the press-fitting degree L of the adjusting pipe 23 for the present adjustment is calculated from the above change rate Kq, there is a possibility that the press-fitting degree L may become too large. The static flow rate represents a flow rate of fluid injected by the injector 1 when the injector 1 injects the fluid continuously for a predetermined period. The static flow rate error Es is an error in the flow rate caused by errors generated in processing steps of parts constituting the injector 1. For instance, the static flow rate error Es is caused by variation in an opening area of the fluid passage at the time when the needle 30 is lifted or by variation in the maximum lifting distance of the needle 30. The dynamic flow rate error Ed represents an error in the flow rate caused by the error in electromagnetic characteristics of the coil 50 and elastic characteristics of the spring 21. Thus, in the conventional adjusting method for achieving the target dynamic flow rate qt based on the change rate Kq of the dynamic flow rate q with respect to the press-fitting degree L of the adjusting pipe 23, the change rate Kq includes the dynamic flow rate error Ed and the static flow rate error Es.
If the press-fitting degree L of the adjusting pipe 23 is too large, there is a possibility that the dynamic flow rate q may become smaller than the target dynamic flow rate qt. The position of the adjusting pipe 23 is fixed by press-fitting. Therefore, if the press-fitting degree L is too large, the adjusting pipe 23 cannot be brought back.
Therefore, in the case where the press-fitting degree L of the adjusting pipe 23 is calculated based on the change rate Kq of the dynamic flow rate q with respect to the press-fitting degree L, a rate of change in the press-fitting degree L per press-fitting process has to be reduced in order not to drive the adjusting pipe 23 excessively during the adjustment of the dynamic flow rate q. Therefore, as shown in FIG. 11, the number of times to drive the adjusting pipe 23 is increased until the dynamic flow rate 1 reaches a standard area Rqt corresponding to the target dynamic flow rate qt and a time length for the adjustment is lengthened. Heavy lines “CHECK” in FIG. 11 represent periods in which the dynamic flow rate q is measured and the press-fitting degree L of the adjusting pipe 23 is calculated.